1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus, and more particularly to an optical scanning device that scans a surface to be scanned with light, and an image forming apparatus provided with the optical scanning device.
2. Description of the Related Art
An optical scanning device has widely been known in association with an image forming apparatus such as a laser printer. The optical scanning device includes a light source, a light deflector, a scanning optical system, and the like. The light deflector has a deflecting-reflecting surface, and deflects light emitted from the light source. The scanning optical system collects light deflected by the light deflector toward the surface to be scanned. A light spot formed on the surface to be scanned moves in a main scanning direction with the rotation of the light deflector. A substantial surface to be scanned is a photoconductive surface of an image bearer.
With recent colorization and increase in operation speed, an image forming apparatus of a tandem system including a plurality of photoconductor drums serving as image bearers has been widespread.
In an image forming apparatus of a tandem system, a plurality of photoconductor drums are disposed along a conveying direction of a recording paper. A plurality of lights emitted from a plurality of light sources, each corresponding to each of the plurality of photoconductor drums, is deflected by one light deflector, split by a folding mirror of a scanning optical system, and guided to the corresponding photoconductor drum to form a latent image. The latent images formed on the surfaces of the respective photoconductor drums are made visible with developers of different colors, sequentially superimposed with one another on the same recording paper, transferred, and then, fixed to become a color image.
Notably, upon an incidence of light emitted from a light source to a light deflector, a system in which light is introduced from an oblique direction with respect to a virtual plane including a normal line of a deflecting-reflecting surface is also referred to as an “oblique incidence system”, and a system in which light is introduced from a direction parallel to the virtual plane is also referred to as a “horizontal incidence system”.
Further, an optical system provided between the light source and the light deflector is referred to as a “pre-deflector optical system”, and a pre-deflector optical system used for the oblique incidence system is especially referred to as an “oblique incidence optical system”.
For example, Japanese Patent No. 4057099, Japanese Patent No. 4098851 and Japanese Patent No. 3450653 describe an optical scanning device using an oblique incidence optical system.
Recently, a compact image forming apparatus with excellent image quality has been demanded. However, the image forming apparatuses provided with the optical scanning devices described in Japanese Patent No. 4057099, Japanese Patent No. 4098851 and Japanese Patent No. 3450653 hardly achieve both miniaturization and improvement in image quality.